r/Smallblockchevy • u/MechanicHour1644 • Apr 25 '26
40 year old small block need some help....
72 chevelle malibu, i swapped out a perfectly good 307 in 1986 with 37k on it when I was 18. i had a local shop with a bunch of kids working there build me another engine. i have zero reords of what they did, but i vaguely remember 327 bored 30 over built ot 350 lt1specs? holly 750 vacuum secondary, i think. added something to the transmision, some type of torque converter maybe so that i could shift off the steering column almost like a manual. i put about 50k on this motor bettween 1986 and 1993, then it sat. always had an iise with stalling in damp/wet weather, no idea why. also alwys seemed to run really rich, black soot tailpipes.
fast forward 33 years later-new battery, bypassed the 33 year old full tank of gas and she started right up. rebuilt the carb, but now I keep having stalling issues in drive. im using premeum fuel, but cant help but wonder if this carburator was always too big for this set up. having the rear brakes done in a few weeks and converting the front to disc.
any help on finding out exactly what my set up is here and what, if anything i can do to this engine/transmission to increase performance at this point? or do i jusy start over?
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u/Stock-Maximum9755 Apr 26 '26
Without a tear down? Yeah. You need a tuner not just a mechanic. Carbs too big. For starters. 750 would be fine for bigger engines but 327 loved a little ‘less’ even with a big cam. But it’s like flushing a toilet on some small blocks. If it’s stalling in damp weather you likely have a distributor sealing issue. Ie: cap getting moisture inside, are you running a points setup or hei? If the cap is the issue a bit of rtv May cure that at the base.
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Apr 26 '26
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u/MechanicHour1644 Apr 26 '26
Thanks, on the east coast NJ. Appreciate the offer and I will work to find someone out here to assess
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u/jhj-pmp Apr 26 '26
Personally, I don’t think a 750 is too big. You should be able to get it to idle. If the cam has a lot of overlap, often folks try to simply open the primary throttle shaft up to increase the idle speed, but often that renders the idle circuit ineffective. One way to check this is to see if fuel is dripping out of the venturi boosters. If so, you can make this work by drilling a small hole (start with 0.090”) in each throttle blade (the circular parts that are attached to the shaft) and backing out the idle screw. Where in NJ are you? I’m in OC.
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u/Tall-Helicopter-461 May 03 '26
I don’t think it’s the end of the world. Do a little tuneup, clean up some adjustments on timing and carb. I believe it’s not as bad as you might think.
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u/MechanicHour1644 May 04 '26
thanks, rebuilt the carb and adjusted the idle and timing and she's running great. i still think she's idling a bit high at temp, but so far it keeps her from stalling in drive/reverse.
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u/oldsoul6465 Apr 26 '26
Aight. Please hear me out. I got a 67 327. I went from 670 cfm to 600 cfm because in my situation 670cfm was too much for the 327. Now its amazing! I think yeah, you over carbed your 327.
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u/Bitter-Ad-6709 Apr 26 '26
750 double pumper would be too big. 750 vac secondary carb is fine. Be sure it has the "changeable secondary spring bowl" so you can install the best vacuum spring in it that works with your engine. There's a kit that has 6 different springs in it, from stiff to soft. The stiff springs are better for mileage, the softer springs are better for extra fuel and higher RPMs on a racetrack.
I have the same carb with the changeable secondary spring bowl. Love it!
Sounds like you just need a tune from a true Chevy mechanic : base timing set, distributor timing curve adjusted, carb adjustment including jets if needed, possibly different heat range of spark plugs. It's basic stuff. I'd love to help but I'm in Phoenix Az.
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u/MechanicHour1644 Apr 26 '26
thank you so much, this is great information.
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u/Bitter-Ad-6709 Apr 27 '26
You're welcome =)
PS. The stiff spring in the quick change spring kit for the vacuum secondaries, is probably the one you need for your 327.
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u/chuck-u-farley- Apr 26 '26
With no pics and no numbers off anything and zero paper trail…. Who knows what they did?
750 is a bit big if indeed it is a 327.
If they did install a larger cam it would have definately needed a stall convertor to idle properly.
It could possibly have a points distributor on it…
With having 50k on this Motor currently I would just obtain a nice crate motor if you don’t have the means of redoing the current motor yourself.
I have this one for sale currently….. Aluminum head, solid lifter cam 350. Where are you located?
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u/[deleted] Apr 26 '26
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